Cut Quality: Solving Dross and Taper Issues

Nothing's more frustrating than watching your plasma cutter complete a job, only to find excessive slag clinging to your parts or beveled edges that don't meet spec. Cut quality issues like dross and taper can turn profitable jobs into costly rework nightmares. The good news? Most cut quality problems have straightforward solutions once you understand what's causing them.

Whether you're running a StarLab CNC plasma table in a professional fabrication shop or your home garage, this guide will help you diagnose and fix the most common cut quality issues: dross buildup and edge taper.

Understanding Dross: The Enemy of Clean Cuts

Dross (also called slag or spatter) is re-solidified molten metal that doesn't blow clear during the cutting process. Instead, it adheres to your workpiece—usually along the bottom edge, but sometimes on top—creating rough edges that require grinding, chipping, or sanding before parts can move to the next phase of production.

While some minimal dross is inevitable with air plasma systems, excessive buildup indicates something in your cutting process needs adjustment.

Types of Dross You'll Encounter

Low-Speed Dross
Appears as a thick, bubbly accumulation resembling a weld bead along the bottom edge. This dross forms when your torch moves too slowly, causing the plasma arc to expand and widen. The gas velocity can no longer effectively blow away all the molten metal, resulting in heavy slag buildup.

Characteristics: Solid bead-like formation, easily removed with a hand scraping tool
Primary cause: Cutting speed too slow for the amperage and material thickness

High-Speed Dross
Shows up as hard, dotted globs of uncut metal on the bottom of the plate. When cutting too fast, the plasma arc lags behind the torch, and the high-pressure gas at the nozzle orifice can't keep up with material removal.

Characteristics: Dotted or beaded appearance, difficult to remove (requires grinding)
Primary cause: Cutting speed too fast for the amperage being used

Top Spatter Dross
An accumulation of re-solidified metal along the top edge of the cut. The swirling plasma jet flings molten material forward instead of down through the kerf.

Characteristics: Light accumulation on top surface, usually easy to remove
Primary causes: Worn consumables, excessive cutting speed, or torch height too high

Corner Dross
Appears at direction changes and tight corners where the machine slows down or dwells. This is a normal occurrence when cutting intricate patterns with many corners.

Characteristics: Minimal accumulation at corners only
Primary cause: Machine slowdown during direction changes

Read More: Troubleshooting Cut Quality